XIV ZOANTHARIA MADREPORARIA 399 



round the mouth. Large specimens may be three-quarters of an 

 inch in diameter. 



TurMnolia is a common Eocene fossil genus found in England 

 and France, and is stated to occur in the Caribbean Sea. The 

 columella stands up like a stylet and the septa are " exsert/' i.e. 

 project above the rim of the theca. 



Trochocyatlius is a genus with well-marked " costae " occurring 

 in tropical shallow water (Fig. 174). 



Fam. 2. Oculinidae. — Colonial forms, dendritic or encrusting, 

 with relatively large and rather prominent calices separated by 

 considerable stretches of compact coenosteum. The zooids bear 

 a crown of ten to forty-eight or more capitate tentacles. 



Neohelia has a fistulose stem lined internally by a horny 

 membrane. There seems to be some reason for supposing that 

 this membrane is formed by the zooids themselves. A similar 

 membrane is found in the fistulose stems of Amphihelia and 

 perhaps other Oculinidae. If this membrane is really formed 

 by the activity of the corals it forms an exception to the general 

 rule that the skeleton of the Madreporaria is entirely calcareous. 

 Others maintain, however, that this membrane is formed by the 

 Chaetopod worms which are found in the tubes, and that the 

 fistulose stem of the coral is formed by folding round and 

 encrusting the horny tubes of the worm. Neohelia is found in 

 the Pacific Ocean.^ 



Lophohelia is a genus forming dendritic colonies of consider- 

 able size. The calices have thick walls and are very deep. 

 Lophohelia prolifera has been found in deep water off the 

 island of Skye and in other localities off- the west coast of 

 Scotland. It is also 'not uncommon in some of the Norwegian 

 fjords and in other parts of the world. 



Oculina is another widely distributed genus found in the 

 shallow tropical waters of the West Indies, the Indian and 

 Pacific Oceans. It forms dendritic colonies of considerable size. 

 The calices are usually arranged in a spiral manner on the 

 branches. The colour of the West Indian species is stated to 

 be light or dark brown when alive. The tentacles are arranged 

 in three cycles, and are usually twenty-four in number. Asexual 

 reproduction takes place by budding at the apex of the branches. 



Fam. 3. Astraeidae. — This is a very large family, and 



' E. M. Pratt, Willey's Zoological Results, pt. v. 1900, p. 591. 



